Few-mode fiber Bragg grating-based multi-wavelength fiber laser with tunable orbital angular momentum beam output

We experimentally demonstrate a multiwavelength fiber ring laser with tunable orbital angular momentum (OAM) beam output. The laser is embedded with a few-mode fiber Bragg grating and a mode selective coupler (MSC). The mode conversion from LP01 mode to LP11 mode is realized by using the MSC as a mode converter. By rotating a polarizer set at the output end of the MSC, the topological charge of the OAM beam can be tuned from l = - 1 to l = +1 and thus a tunable OAM beam is obtained. By adjusting the polarization controllers (PCs), the laser can operate under single-, dual- and triple-wavelength lasing conditions.